Abstract:
With the steady growth in world electricity demand, there has been a drastic increase in the demand for renewable energy sources. Wind being a clean, free and inexhaustible energy source is one of the fastest developing renewable technologies. Initially, in wind energy conversion systems, squirrel cage induction generators directly connected to grids were used. But, in such systems the pulsations in wind power directly affected the grid quantities. Also, they could be operated only at a particular speed; hence, their efficiencies were low. But with the advancement in the field of power electronics and introduction of other type of generators, the wind energy conversion systems have become much more efficient. With the introduction of ariable speed wind turbines , wind energy conversion systems have become much more efficient as they offer effective power capture for a wide range of speeds when compared to the fixed speed wind turbines. Doubly fed induction generators and permanent magnet synchronous generators are most preferred generators for variable speed wind turbine operation. In this thesis, Doubly fed induction generator based wind energy conversion system has been discussed in detail. The operation of DFIG in sub-synchronous and super-synchronous region is studied. The operation and control of the back-to-back PWM converters that are required to connect the rotor side of the generator to the grid has also been studied in detail. The control of the rotor power converters is performed using three control schemes: traditional PI controllers, Fuzzy logic controllers and finally sliding mode control in MATLAB simulink. The performance of the system under these control schemes is observed and compared. Optimum tip speed ratio method is used for maximum power capture. The response of system namely, grid current and power factor, stator and rotor currents, stator power factor, stator and rotor powers, DC link voltage for different wind speeds such that the generator operates in sub-synchronous and super-synchronous mode is shown in simulation results for all the three control schemes
